The best version of the Shark Shield for spearfishing, in my opinion, is the Freedom 2 or 4 unit. The electronics and battery are in a neoprene pouch that is strapped to your calf. From this pouch extends a seven foot long tether antenna containing two electrodes, which trails unobtrusively behind the diver. I like this unit because it is easy to take on and off between dives and there is no interference with your kicking, you tend to almost forget it is there. The manufacturer says Freedom 4 is fast becoming the most popular unit for those who dive. Freedom 2 has a 2 hour battery pack, whereas the Freedom 4 has a 4 hour battery. I was an early adopter of this technology, having used it now for almost two years. I usually leave the Shark Shield turned off until I spear a fish, unless I already see sharks or the visibility is low. The Shark Shield can shock you and your fellow divers if the tether antenna is touched, but the tingle is not a bad shock.
The electric pulse the Shark Shield puts out every half-second only affects sharks, rays and skates. Other fish and marine creatures are not disturbed. It does not scare away the fish we are seeking to spear and it does not attract sharks to you. The effective protective range in my observations starts about ten to fifteen feet away as the shark approaches. His initial discomfort increases as he gets closer until it becomes intolerable. The shark then veers away. The bottom line is that this is a great product that works well. I will not leave home without it. The Shark Shield is the best solution for spearfishing with sharks on the market today.